The demand for energy storage devices with improved performance and safety characteristics has increased with the development of new technologies requiring batteries as power sources. A wide range of electrochemical characteristics must be accommodated for these new technologies. Some critical characteristics that power sources must accommodate are energy density, low temperature performance, high rate capability, low cost, reliability, and safety. A key objective is to develop a battery chemistry to meet required power source characteristics of new equipment technologies. An important objective in developing a practical rechargeable lithium battery is to have a cathode/anode combination that is stable with the electrolyte and provides energy with excellent cycle-life and rate capabilities.
The class of lithium intercalating transition metal oxides are particularly attractive as active materials for positive electrodes of rechargeable lithium batteries because of their inherently high energy content and ability to reversibly intercalate lithium ions at remarkably high rates. However, these materials are so highly oxidizing that very few electrolyte solvent combinations are stable with these electrodes. In particular, most ether solvents that are used very effectively in lithium battery applications have too low an oxidation potential for an electrode such as Li.sub.x CoO.sub.2. Some ester solvent based electrolytes have been found to perform well with the Li.sub.x CoO.sub.2 cathode but the lithium anode cycling efficiency is typically low in these electrolytes.